(i) Field of the Invention
The present invention relates to an L-type catalyst containing a platinum component, one or more halogen components and one or more metals selected from the group Ib of the periodic table, a method for preparing this catalyst, and a method for producing aromatic hydrocarbons and a gasoline having a high octane number by the use of the catalyst. More specifically, the present invention relates to a catalyst suitable for the production of aromatic hydrocarbons and a gasoline having a high octane number, a method for preparing the catalyst, and a method for efficiently producing aromatic hydrocarbons and a gasoline having a high octane number by the use of the catalyst. The employment of this catalyst can restrain a cracking activity and the formation of coke, and can also improve an aromatic selectivity and a liquid yield.
(ii) Description of the Related Art
Heretofore, as catalysts for aromatizing non-aromatic hydrocarbons such as aliphatic hydrocarbons to produce aromatic hydrocarbons, platinum-aluminum catalysts have been used. However, these catalytic systems have a drawback that hydrocarbons having 6 and 7 carbon atoms cannot effectively be converted into the aromatic hydrocarbons.
Thus, in recent years, as a catalyst in which this drawback has been overcome, there has been found a catalyst in which platinum is supported on an L-type zeolite (Japanese Patent Publication No. 57408/1983). In this catalyst, a metal in the group VIII of the periodic table is supported on the L-type zeolite, but its activity is not sufficient and its life is inconveniently short. Afterward, for the sake of the improvement of the activity, a selectivity and the catalytic life and the simplification of a catalyst preparation method, various techniques have been suggested. For example, there have been suggested (1) a method which comprises supporting a metal in the group VIII on an L-type zeolite, and then subjecting it to an oxy-chlorination treatment to improve the catalytic activity and the life (Japanese Patent Application Laid-open No. 168539/1985), (2) a method which comprises treating an L-type zeolite with a solution containing a platinum salt and a non-platinum salt to improve platinum dispersion (Japanese Patent Application Laid-open No. 138539/1986), (3) a platinum catalyst supported on L-type zeolite treated with a halogen-containing compound (Japanese Patent Application Laid-open No. 57653/1987), (4) a platinum catalyst supported on L-type zeolite treated with a halogen-containing compound (Japanese Patent Application Laid-open No. 91334/1988), and (5) a simple catalyst preparation method which comprises the step of simultaneously supporting and treating a platinum component and one or more halogen components on an L-type zeolite (Japanese Patent Application Laid-open No. 49936/1993).
However, the above-mentioned method (1) has a drawback that a treating apparatus is complex, and the method (2) has a drawback that the catalytic activity is not sufficient. In addition, the catalysts of the above-mentioned (3) and (4) make use of Freon which is a harmful substance in a halogen treatment, and they have a drawback that a high-temperature treatment is carried out, so that dealumination takes place and hence a surface area decreases. Moreover, in the above-mentioned method (5), there is a drawback that the obtained catalyst has a high cracking activity.
As understood from the foregoing, each of the conventional catalysts in which platinum is supported on the L-type zeolite has the disadvantage, and for the reason, they have not been always sufficiently satisfactory.